diff --git a/core/java/android/content/SharedPreferences.java b/core/java/android/content/SharedPreferences.java index d4f7f06b008d1..00c2d8f78055e 100644 --- a/core/java/android/content/SharedPreferences.java +++ b/core/java/android/content/SharedPreferences.java @@ -355,7 +355,14 @@ public interface SharedPreferences { /** * Registers a callback to be invoked when a change happens to a preference. - * + * + *

Caution: The preference manager does + * not currently store a strong reference to the listener. You must store a + * strong reference to the listener, or it will be susceptible to garbage + * collection. We recommend you keep a reference to the listener in the + * instance data of an object that will exist as long as you need the + * listener.

+ * * @param listener The callback that will run. * @see #unregisterOnSharedPreferenceChangeListener */ diff --git a/docs/html/guide/topics/ui/settings.jd b/docs/html/guide/topics/ui/settings.jd index d96447dc032f8..30b7eecc785fb 100644 --- a/docs/html/guide/topics/ui/settings.jd +++ b/docs/html/guide/topics/ui/settings.jd @@ -820,7 +820,8 @@ public class SettingsActivity extends PreferenceActivity public static final String KEY_PREF_SYNC_CONN = "pref_syncConnectionType"; ... - public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) { + public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, + String key) { if (key.equals(KEY_PREF_SYNC_CONN)) { Preference connectionPref = findPreference(key); // Set summary to be the user-description for the selected value @@ -863,7 +864,40 @@ protected void onPause() { } +

Caution: When you call {@link +android.content.SharedPreferences#registerOnSharedPreferenceChangeListener +registerOnSharedPreferenceChangeListener()}, the preference manager does not +currently store a strong reference to the listener. You must store a strong +reference to the listener, or it will be susceptible to garbage collection. We +recommend you keep a reference to the listener in the instance data of an object +that will exist as long as you need the listener.

+

For example, in the following code, the caller does not keep a reference to +the listener. As a result, the listener will be subject to garbage collection, +and it will fail at some indeterminate time in the future:

+ +
+prefs.registerOnSharedPreferenceChangeListener(
+  // Bad! The listener is subject to garbage collection!
+  new SharedPreferences.OnSharedPreferenceChangeListener() {
+  public void onSharedPreferenceChanged(SharedPreferences prefs, String key) {
+    // listener implementation
+  }
+});
+
+ +

Instead, store a reference to the listener in an instance data field of an +object that will exist as long as the listener is needed:

+ +
+SharedPreferences.OnSharedPreferenceChangeListener listener =
+    new SharedPreferences.OnSharedPreferenceChangeListener() {
+  public void onSharedPreferenceChanged(SharedPreferences prefs, String key) {
+    // listener implementation
+  }
+};
+prefs.registerOnSharedPreferenceChangeListener(listener);
+

Managing Network Usage

@@ -1142,13 +1176,15 @@ protected Parcelable onSaveInstanceState() { final Parcelable superState = super.onSaveInstanceState(); // Check whether this Preference is persistent (continually saved) if (isPersistent()) { - // No need to save instance state since it's persistent, use superclass state + // No need to save instance state since it's persistent, + // use superclass state return superState; } // Create instance of custom BaseSavedState final SavedState myState = new SavedState(superState); - // Set the state's value with the class member that holds current setting value + // Set the state's value with the class member that holds current + // setting value myState.value = mNewValue; return myState; }